Propeller pitch changing mechanism



s P 4, 1956 R. c. TRESEDER ETAL 2,761,518

PROPELLER PITCH CHANGING MECHANISM Filed Sept. 8, 1951 7 Sheets-Sheet 1 ACTUATOR UNIT COORDINATING MECHANISM FUEL CONTROL.

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PROPELLER PITCH cmmcmc MECHANISM Filed Sept. 8. 1951 7 Sheets-Sheet 2 /N VENTO ES 20M g g I %u P 1956 R. c. TRESEDER ETAL PROPELLER PITCH CHANGING MECHANISM Filed Sept. 8, 1951 Sept. 4, 1956 R. c. TRESEDER E'lAL.

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PROPEILLER PITCH CHANGING MECHANISM Filed Sept. 8, 1951 7 Sheets-Sheet 5 [7/ 106 2724 $196 274 V j \tpi I %75 i/M cz ita v| iz we 24f #7 199 6 vu ig 2m 26/ (If, My %76 I 264, g Z85, L VHI I?! J5 76 i 6 7/ Z92 //vvE/\/T02s I Z3 2 I56 36! Z4 7 264 7 194 1- 1 fiw mm if F 1% 2 7/ g m #M 2;: 174 W J95 7 w xiTro/e NE vs United States Patent PROPELLER men CHANGING MECHANISM Robert C. Treseder, Dayton, James R. Kessler, Vandalia,

and Robert K. Skinner, Dayton, Ohio, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Application September 8, 1951, Serial No. 245,671

21 Claims. (Cl. 170-16017) This invention relates to internal-combustion-turbinepropeller power plants for aircraft use.

The objects of the invention include provision of control of turbine speed through control of propeller pitch by the use of apparatus which is manually controlled to seelct a desired speed and which operates automatically to maintain a selected speed within relatively close limits when speed governing is desired.

A further object of the invention is to provide for feathering and unfeathering of the propeller blades, for control of blade angle in a certain low pitch range without governing action when positive or negative thrust is desired.

To accomplish these objects, it is a further object to provide a propeller pitch controlling apparatus capable of being conditioned by a pilots control lever which, in a portion of its range of movement known as the governor control range, causes a governor to be' conditioned to maintain a selected speed and which by movement of the lever from the governor control range toward one limit of its movement, interrupts control by the governor and causes the blade pitch to be adjusted to certain low positive values which diminish to zero and then increase negatively to a certain value. Another manually operated device is provided for eifecting interruption of governor control and for effecting feathering and unfeathering. In this connection, a further object is to provide for conditioning the propeller pitch controlling apparatus to effect the results above described by the use of an electric servo-motor which is under control by the pilots control lever.

Another object is to prevent improper adjustment of blade pitch in case of mal-functioning or non-functioning of that part of the apparatus which governs to a selected speed. Therefore means are provided for discontinuing blade pitch control by the governor when it begins to function in an abnormal manner so that other components of the apparatus will be allowed to take over control of blade pitch to prevent over-speeding or underspeeding of the turbine.

Another object is to provide control apparatus of the kind described which can be used in a power plant comprising two turbines which may operate together or separately to drive one propeller. With each turbine, there is associated a pilots control lever which controls the turbine fuel. Therefore an object is to provide a blade angle controlling apparatus capable of operation by the pilots control lever of either turbine and brought under control by the selected pilots lever merely by a movement thereof relative to the other lever which is not used to control.

To accomplish these objects, the disclosed embodiment of the present invention includes a self-contained hydraulic apparatus located within the propeller hub and capable, by itself, of automatic control of blade angle to prevent overspeeding and under speeding and capable of direct manual control for feathering and unfeathering and for adjustment to obtain positive blade angle in a ice relatively low range and to obtain negative blade angle, and includes electrical apparatus located principally outside of the hub and capable of effecting control of the hydraulic apparatus for the purposes described until disabled by accident, combat or other reasons.

A further object of the invention is to provide a system which includes two differentially acting solenoids, means for impressing, alternately upon the solenoids, electrical impulses which may be equal or different in duration depending on factors which are sensed by the impulsing means and means responding to the improper functioning or the non-functioning of the impulsing means for discontinuing its effect upon the solenoids.

Further objects and advantages'of the present invention will be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of the present invention is clearly shown.

In the drawings:

Fig. 1 is a schematic layout of an hydraulically controlled propeller and the attendant control mechanism constituting part of the instant invention.

Fig. 2 is a schematic diagram of the control circuit Schematic layout Referring particularly to Fig. 1, the propeller is composed of a plurality of pitch controlled blades 5 journalled in a hub 6 supporting a hydraulic regulator 7. An engine driven alternator 8, here shown in conjunction with the regulator 7, feeds by a conduit 9 into a unit 10 which includes an electric governor. Unit 10 is connected by wires in conduits 11 and 12 with an actuator 13 which, through a connection 14, is under control by a coordinator 15 having a fuel control 16. A pilots control lever 17 is connected by cable 18 to the coordinator 15. The actuator unit 13 has a mechanical connection 18a with a control lever 19 on the hydraulic regulator. The control unit 10 is electrically connected by cable 20 and slip ring engaging brushes 29a with an electro-hydraulic valve 21 carried by the regulator 7 and connected into its hydraulic circuit.

The control of propeller blade pitch accomplished by the hydraulic regulator will be apparent from the operation of the fluid circuit illustrated in Fig. 2. Governing is normally accomplished thru the electric governor in conjunction with valve 21, control by underspeed and overspeed governors being provided to overcome any offspeeds which are beyond the correction capacity of electric governor and the valve. The propeller with its controls is basically a constant speed unit with provision made for feathering and unfeathering and for blade angle control in the ranges of negative thrust, starting, and ground idle as well as shifting from one regime to the other.

Hydraulic system As shown in Fig. 2, the regulator is provided with three pumps 22, 23 and 24. Pump 22 has a capacity provided to supply oil for all normal governing, and pump 23 has a capacity to provide a supply of oil for any large pitch changes and only when the pump 22 is unable to provide necessary volume and pressure of oil to supply the demand called for. Normally, the output of pump 23 is returned directly to the reservoir. By propeller rotation the pumps 22 and 23 are driven and feed into lines 25 and 26 respectively. As shown in the drawing, flow from the pump 22 after passing thru a check valve 27 flows to a trunk line 28 and is directed to a pressure control valve assembly 29. This assembly is composed of three valves, a pressure relief element 30 which acts as a safety valve, an equal area valve 31 Which determines the pressure for the system on a pressure demand basis since one side 32 is directly connected to the pressure in blade actuating servo 33 thru a shuttle valve 34. The third valve is the simple shuttle valve 34 which applies the largest pressure in the blade actuating servo unit 33 to the side 32 of the equal area valve. The opposite side 35 of the equal area valve is always subject to pressure in the trunk line 28 thru branch 36. The excess pressure on the side 35 of the equal area valve, which is above that called for by the pressure control valve assembly, exhausts thru the port 37 and flows thru passage 38 to a chamber 39 of a flow control valve 40 controlling the connection from pump 23 to the trunk line 28. As long as there is flow from the pressure control valve assembly 29 thru the branch 38 there will be sufficient pressure in chamber 39 to compress a spring 41 and move the valve 42 for connecting pump outlet 26 with an exhaust port 43. When the system pressure drops to the point where no oil is being bypassed to the passage 38 by the pressure control valve assembly 29, then there is no longer any pressure delivered to the chamber 39 of the flow control valve and the spring 41 repositions the valve 42 in such manner that the output of the pump 23 passes thru check valve 44 and flows into trunk line 28, said flow being added to the system pressure from pump 22. The pump flow control valve 40 therefore senses when the system pump 22 no longer has a capacity to meet the demands of the system and then adds the output of the pump 23 to the pump line 28. When the system pressure has been built up sufliciently the flow control valve again returns the output of the pump 23 to the reservoir or supply cavity within the regulator. The equal area valve 31 has unrestricted connection by a passage 45 with the relief valve 30 whose exhaust is also connected by loop 46 to the passage 38. Thus, the entire system is safeguarded, and the auxiliary pump 23 is cut out of the system should the pressure in the trunk line reach a value in excess of a predetermined amount.

The third pump 24 is driven by an electric motor diagrammatically illustrated at 47 enclosed within a housing 48 to which drain of practically all of the control valves returns, there being a centrifugally controlled valve assembly 59 which insures that the pump will always be primed by reason of drain fluid from the valves being contained in sump 51 connected with the inlet 52 to the pump 24. Discharge of the pump 24 leads by passage 53 to a check valve 54 and by branch 55 to a groove 56 of a feather pump control valve 57. A chamber 58 of this valve assembly is always exposed to the trunk line pressure 28 thru a passage 59. If the potential of pressure in trunk line 28 is above the predetermined minimum value, the valve stem 60 moves to connect branch 55 with a drain passage 61 leading back to the sump 51. If the pressure in chamber 58 is below predetermined value, the valve stem 60 is so moved by the spring 60a as to close the exhaust passage 61 such that the pump delivery thru 53 must then pass thru the check valve 54 into the trunk line 28. Therefore the feathering pump 24 when operative can only exhaust into trunk line 28 if the potential of pressure therein is less than the predetermined value. The feathering pump 24 is under control of the control unit 10 by which the motor 47 can be energized only when the propeller speed is less than a predetermined value; and it is used to complete feathering, start unfeathering and to provide hydraulic pressure for control of blade pitch to any degree when the propeller is not rotating.

System pressure in the trunk line 28 is led to the pressure port 62 of the solenoid valve 21. All normal governing is accomplished thru the operation of this valve which is controlled by the control unit 10 and the elements thereof shown in Figs. 3 and 4. This valve 21 is the instrument by which electrical signals of the control unit 10 are caused to eifect a control upon the hydraulic system in the regulator. The valve is composed of a plunger 63 having lands 64, 65 disposed on either side of the source port 62 and normally closed control ports 66, 67 leading by passages 68, 69 to pitch change passages 71, 72 communicating with chambers 73, 74 of the servo motor 33. A pair of solenoids 75, 76 at opposite ends of the plunger 63 have a ground connection at 77 and control leads 78, 79 leading to switch terminals 80, 81. When, for example, solenoid 76 is more effectively energized than 75, the valve plunger 63 is pulled right in Fig. 2 to connect source port 62 with the increase pitch line 69 which actuates the blade servo in a pitch increasing direction by applying the pressure in trunk line 28 to chamber 74. Drain back from the chamber 73 flows thru 71 and 68 to exit thru port 66 to be returned to the reservoir. When the pressure is applied to passage 69, a feed back passage 82 connecting with shuttle valve 34 moves a plunger 83 so that the pressure applied to increase pitch chamber 74 is also applied thru branch 84 to the chamber 32 of the equal area valve, thereby increasing the potential of pressure in the trunk line 28 to satisfy the needs in the control force applied by the solenoid valve to the increase pitch chamber 74 of the blade servo motor. When the other solenoid is more effectively energized, the valve piston 63 is pulled left in Fig. 2 so as to connect the source port 62 with the decrease pitch passage 68 leading to blade servo chamber 73. At the same time the feed back passage 85 delivers increase pitch pressure to the shuttle valve 34 so that 83 is moved to permit the pressure in feed back 85 to follow thru 84 to the chamber 32 of the equal area valve. The pressure of trunk line 28 is again stepped up to meet the demands of pressure for shifting the blade in a decrease pitch direction. Both of the solenoids are energized selectively and proportionately by the control mechanism shown in Figs. 3 and 4 and applied thru the brush and slip rings 20a which lead to switch points 86 and 87 of a centrifugally actuated switch 88. The switch 88 has a pair of conductors normally engaging contacts 89 and 90 which connect by cable 91 with the windings of feathering motor 47. One of the wires of this cable 92 extends directly from one of the brushes and slip rings 20a to the windings of the motor, as will presently appear. Leads 93 and 94 extend from separate brushes and slip rings 20a to the movable elements of the switch 88 and when the propeller speed reaches a predetermined value, say 250 to 300 R. P. M., the switch 88 moves to connect leads 93 and 94 to terminals 80 and 81 respectively.

During governing at approximately the correct speed the solenoids 75, 76 will be energized alternately with equal dwell on opposite sides, the control being eliected by a longer dwell in one direction than the other. This continuous oscillation of the valve plunger 63 by the alternate energization of the solenoids provides jitter at the governing speeds which minimizes any tendency of the valve to stick and thereby substantially reduces or eliminates static friction. Springs (not shown) are incorporated in the valve which center the valve plunger 63 when neither solenoid is energized. The solenoid valve 21 is capable of efiecting a maximum pitch change rate of 6 per second which is well within the flow rate provided by the system pump 22.

The solenoid valve 21 which accomplishes normal governing must be highly sensitive in order to provide extremely fine governing, and its capacity is necessarily limited. A pitch change of 6 per second gives a capacity that is adequate for all but a very few governing problems, but may be insufficient for an extremely rapid throttle change such as in a carrier wave-off, or in a violent acrobatic maneuver. Some of the abnormal opcrating conditions of the turbine that should be avoided include large over-temperatures, overpseed, and underspeed.

In order to eliminate the possibility of severe overspeeds an overspeed governor 95 is incorporated in the hydraulic system enclosed within the regulator. System pressure from the trunk line 28 is applied thru branchZSa to a source port 96 and to a groove between lands 97 and 98 of the valve plunger 99. The valve plunger 99 is articulated to a lever 100 which has a fixed fulcrum 101 and a fixed stop 102. The plunger and lever 99, 100 are under the urge of a spring 103 to engage the fulcrum 101 and stop 102 so that lands 97 and 98 normally cover ports 104 and 105. Centrifugal force of a predetermined value may operate on the plunger 99 and lever 100 to raise the lever from its stop 102. The stop 102 preprevents this governor acting as an underspeed governor, and the spring 103 insures that the governor 95 will have no efifect until a speed predetermined by the spring pressure is reached. At that time fluid pressure from the trunk line 28 passes from port 96 to port 104 and thence by passage 106 thru selected passages of a selector valve 107 to the increase pitch line 72 leading to the blade angle servo motor 33 giving an extremely rapid pitch change. Return from the opposite side of the servo motor 33 passes by way of the control passage 71 thru the selector valve 107 and by passage 108 to port 105 of the overpseed governor valve 95. From there it passes by port 109 into drain passage 110 which leads back to the sump 51 for priming of the feathering pump 24 and thru the motor housing 48 for cooling the motor 47. At any speed below maximum control speed the overspeed governor piston 99 closes off both ports 104 and 105 leading to the blade angle servo motor and thereby prevents loss of pressure to the overspeed governor.

Since the overspeed governor must not interfere with normal governing it is adjusted so that it will not come into efiect until a turbine speed is reached that is a little above maximum control speed.

In order to prevent possibility of severe underspeeds, an underspeed governor 111 is included in the hydraulic system of the regulator and has a supply port 112 connected with the trunk line by a branch 28b. It is similar to the overspeed governor in that a fixed fulcrum 113 supports a lever 114 against the urge of a spring 115, while a fixed stop 116 prevents action as an overspeed governor. The lever 114 is articulated with a valve plunger 117 having lands 118 and 119 spaced to coincide with ports 120, 121 when the lever 114 is disposed against the stop 116 by reason of centrifugal force. This governor is so adjusted that it will act at approximately 12,300 turbine R. P. M. or at a value below minimum control speed. With system pressure applied to port 112, a drop of speed below the underspeed governor setting results in a decrease of centrifugal force to the point that spring pressure 115 moves the lever 114 away from.

the stop 116 which allows the pressure at 112 to flow thru port 120 into passage 122 which joins 108 and flows thru the selector valve 107 to the decreased pitch passage 71 leading to the blade angle servo 33. Return flow from the other side of the servo is directed thru control passage 72, the selector valve 107 and passage 106 and extension 123 to port 121 of the underspeed governor valve 111. From there the fiow passes by the axial passage 124 of the plunger 117 to communicate with drain port 125 from which it communicates with the drain passage 110 and hence finds its way to the pump sump 51 as in the case of the overspeed governor valve. During any speed above the setting of the underspeed governor the plunger 117 closes 011 both lines 122 and 123 and hence 106 and 108 leading to the chambers of the blade angle servo motors, and therefore prevents any pressure loss thru the underspeed governor.

The regulator governing, accomplished by the solenoid valve 21 with the overspeed governor 95 and underspeed governor 111, is supplemented by a blade angle control between certain limits which solves several unique problems encountered in certain operations. In the case of negative thrust and on account of large idle speeds, any blade angle capable of absorbing full power at rated speed still delivers considerable thrust at idle speed, and necessitates control of the fuel governor in addition to a controllable blade angle. In this blade angle control range the hydraulic regulator is capable of selecting any blade angle from -22 to +10 at the will of the pilot. The fuel governor will automatically give the proper turbine speed at all times in the negative thrust range thru the action of the control 16 of the coordinator 15. The amount of thrust is then determined by the blade angle selected by the pilot with the turbine automatically maintaining proper speed. One lever 17 is used for each power section and the position of this lever acting thru the coordinator 15 automatically controls both turbine and propeller throughout all ranges by the control connections 16 and 14 respectively.

The selector valve 107 within the regulator is actuated when it is desired to operate under blade angle control. In the selector valve, a plunger 126 having spaced lands 127, 128 and 129 is urged by spring 130 to such position as to connect passage 106 with 72 and 108 with 71 whereby the control ports of the overspeed governor 95 and the underspeed governor 111 are connected to the blade angle servo motor 33 in the same sense that control passages 69 and 68 of the solenoid valve 21 are connected. This selector valve in its normal position therefor allows passage of fluid from either overspeed or underspeed governors to the blade angle servo. When it is desired to enter the blade angle control range the valve plunger 126 is moved to a position such that the lines 106 and 108 from the overspeed and underspeed governor are blocked 011 and such that the control passages 71 and 72 are connected with ports 131, 132 respectively leading by passages 133, 134 to ports 135, 136 of a blade angle distributor valve 137. A selector control servo valve 138 having a plunger 139 with channel 140 is always open to trunk line pressure thru passage 28c and has a port 141 connected by passage 142 with an actuating chamber 143 at the end of a selector valve 107. When the pilots control lever 17 is moved into the blade angle control range the control of the solenoid valve 21 by the control unit 10 is cut out and the servo valve 138 is actuated by movement of the regulator control ring 19 which acts thru linkage 144 to shift a cam plate 145 that operates upon the valve plunger 139 to move it from the governing position illustrated in Fig. 2 to the B. F. position (blade angle or feathering) whereby passage 280 is connected with groove 140, port 141, passage 142 and the actuating chamber 143 of the selector valve 107.

The valve plunger 126 is then moved to the position for connecting the ports 135, 136 of the distributor valve to the passages 71 and 72 respectively leading to the blade angle servo 33. When the pilots control lever 17 is moved out of the blade angle control range, the servo valve 138 cuts off the fluid pressure from the end of the selector valve 107 and the spring pressure returns the selector valve to its normal position thereby cutting out the distributor valve 137 and reconnects the underspeed and overspeed governors. Fluid pressure from the trunk line 28 is continuously applied to the supply port 146 of the distributor valve 137 thru branch 28d. When the blade angle control range is entered, the regulator arm 19, while actuating the servo valve 138, also moves a control ring 147 that swings an arm 148 about a yoke 149 (threadedly engaged by a blade angle feed back shaft 150) to actuate a cam 151 of a lever 152 articulated to a valve plunger 153 in the distributor valve 137. The lever 152 is urged against the arm 148 by a spring 154, and the valve plunger 153 has spaced lands 155 and 156 adapted to stop the ports 135 and 136 leading to control passages 133 and 134.

If the pilots control lever 17 is moved into the negative pitch portion of the blade angle control range, the regulator lever 19 acts thru 144 to move the ring 147 and cam 145 accordingly. The ring 147 acting thru the arm 148, yoke 149 and cam 151 positions the distributor valve plunger 153 so as to connect the decrease pitch port 135 with a supply port 146. The fluid passes thru passage 133 to port 131 of the selector valve 107 and thence thru control passage 71 to decrease pitch chamber 73 of the blade angle servo motor 33. Return fluid from chamber 74 passes by way of 72 to the selector valve 197 and thru port 132 and passage 134 to port 136 of the distributor valve. From thence it flows thru the drain port 157 communicating with drain passage 110 that leads back to the sump 51 of the feathering pump 24-. As the angle of the blade 5 decreases due to the flow of fluid applied to the chamber 73, the feed back screw shaft 150 repositions the yoke 149 which repositions the distributor valve plunger 153 by follow-up action effected by the arm 148, cam 151 and spring 154, thereby cutting off the flow of fluid when the blade an le has reached the position dictated by the pilots control lever 17. The opposite of the above occurs when the pilots control lever is moved in the opposite direction, except that return oil from the blade angle servo motor 33 passes from the selector valve port 131 thru passage 133, port 135 of the distributor valve and thence thru a hollow passage in the plunger 153 to the drain port 157. Thus any blade angle from 22 to 10 may be selected by the pilot by the proper positioning of the cockpit control lever 17 within the blade angle control range.

A restrictor valve 160 is connected into each branch 28a, 28b, and 28c leading to the pressure supply ports of the overspeed governor 95, the underspeed governor 111 and the distributor valve 137, in order to maintain a minimum pressure in the trunk line branch 28c that is sufiiciently greater than what is needed to actuate and hold open the selector valve 107 against the urge of the spring 130. The term restrictor valve as herein used refers to a check valve structure which assures a minimum pressure potential in trunk line 280. This minimum pressure is substantially above what is required to actuate the piston of the blade angle servo motor 33, and insures that during a large blade angle change the system will not be bled to a point insufficient to actuate the blade angle servo piston. The restrictor valves 160 will not open to admit pressure to the distributor valve 137 unless the pressure is adequate to keep the selector valve open whenever pressure is admitted to the servo valve 138.

A solenoid stop 16011 is provided which must be retracted before the regulator control lever 19 may be moved into the blade angle control range, thus preventing inadvertent entry into that range.

A hydraulic lowpitch stop is provided at +l by means of the feed-back shaft 150. That feed-back shaft 150, acting thru the yoke 149, repositions the distributor valve cam 151 while operating in the blade angle control range as the blades change angle in response to initial movement of the cam. The feed-back shaft 150 also operates so that, as the blade an le decreases in the governing range, an extension 150a thereof will move a stop 161 under the valve plunger 99 of the overspeed governor 95 when the blade angle reaches +10". If the angle of the blade tries to decrease beyond this point without the pilots control lever 17 having been moved to the blade angle control range, then the stop 161 moves the valve plunger 99 to a position causing pressure from port 96 to flow thru the port 104 and passage 106 to the.

increase pitch side 74 of the blade angle servo 33 until sufiicient increase blade angle chan e has been obtained to cause the feed-back shaft 150 to permit the overspeed governor plunger 99 to assume its normal position, thus cutting off further fluid flow. Thus, the feed-back shaft 150, and stop 161 of the overspeed governor provide a hydraulic low-pitch stop at Though the solenoid valve 21 may still be calling for decrease pitch, the overspeed governor has suflicient capacity to override the solenoid valve and substantially prevent the blades from moving below an angle of +10". In other words, the feedback mechanism positions stop, or cam, 161 so that if the pitch position of the propeller blades moves to an angle below a positive 10", fluid under pressure will be applied through port 104 and lines 106 and 72 to the increase pitch chamber 74 of the servomotor 33. Thus, the hydraulic low pitch stop arrangement merely prevents the propeller blades from moving to an angle appreciably below a positive 10 during constant speed propeller operation. The feed-back shaft 150 actuates the overspeed governor in the same manner when the pilots control lever is in the blade angle control range, but as the pilots control lever 17 is moved into the blade angle control range the selector valve 107 cuts out the overspeed governor and permits the distributor valve 137 to take over the control. By this means the hydraulic low-pitch stop is removed when entering the blade angle control range.

All electrical power sources are remotely mounted from the propeller and supply electrical power to the solenoid valve and other devices thru the slip rings and brushes 20a. One of these slip rings has a ground in the propeller regulator at 162 by reason of which an interregulator ground of the solenoid valve at 77 and such other electrical devices as are included may be made to the regulator structure. The motor 47 driving the feathering pump 24 need not be connected while the propeller is turning at any appreciable speed since the other pumps 22 and 23 will supply all the fluid flow and pressure that is needed. The solenoid valve 21 need only be supplied with signals when the propeller is rotating within the governing range. The centrifugal switch 88 is therefore used to shift from the feathering motor circuit to the solenoid valve circuit under the specified conditions. The centrifugal switch will cut out the solenoid circuit and will cut in the feathering motor circuit at a specified R. P. M. which is well below the governing range, but the centrifugal switch will not in itself cause any feathering of the propeller.

Feathering of the propeller may be accomplished with the cockpit control lever 17 in any position. In the feathering operation the actuator 13 which contains a motor 163 (Fig. 3) normally positions the regulator control arm 19 in accordance with signals received from the coordinator unit 15 and the signals relayed by the coordinating unit are determined by the position of the cockpit control lever 17. However, when a feathering switch 164 (Fig. 3) in the cockpit is pushed left, the actuator unit 13 is automatically removed from under control by the coordinating unit 15, and the actuator 13 is caused to move the regulator control arm 19 (Fig. 2) to the feather position. Pushing the feathering switch 164 in also operates a relay GT (Fig. 4) which cuts out the governing signals to the solenoid valve 21 and operates a relay S which cuts off fuel to the turbine unit. Movement of the regulator control arm 19 to the feathered position causes actuation of the servo valve 138 to cause pressure fluid to flow to the selector valve chamber 14-3. The selector valve plunger 126 is moved against the action of the spring 130 to block off the overspeed and the underspeed governors and to connect the ports and 136 from the distributor valve 137 to the control passages 71 and 72 respectively. Movement of the regulator arm 19 also positions the cam 151 of the distributor valve so that the valve plunger 153 is moved to a position allowing fluid pressure to flow from 146 to 136 and by passage 134 to the selector valve port 132 and thence thru passage 72 to the increase pitch side 74 of the blade angle servo 33. The feed-back shaft 150 cannot reposition the cam 151 before the feather position is reached. Return flow on the other side 73 of the blade angle servo passes thru the selector valve port 131 and thru the hollow piston of the distributor valve to exit at 157 by which it returns to the sump 51 of the feathering motor 24. The regulator pumps 22 and 23 supply fluid under pressure until the speed of propeller rotation drops below the setting of the centrifugal switch 88. At this point the centrifugal switch 88 shifts from contacts 80, 81, to contacts 89, 90 for energization thru the cable 91 tothe feathering motor 47. The feathering pump flow control valve 57 closes the exhaust port 61 and thereby insures that the flow from the feathering pump 24 will pass thru the check valve 54 and enter the fluid pressure pump line 28. The feathering pump flow control valve is, designed so that a regulator system pressure in the trunk line 28 of more than 500 p. s. i. moves the valve piston 60 to a position that vents the output from the feathering pump back to the feathering pump reservoir or sump 51. When the system pressure drops below 500 p. s. i., the spring of the control valve 57 moves the plunger 60 to a position where exhaust port 61 is closed so that the output of the pump is directed into the trunk line 28 thru the check valve 54. A time delay relay TD (right portion of Fig. 3) operates to hold the pilots feathering switch 164 in the feathering position long enough for the blades to reach the feathering position. When the regulator control arm 19 is in the feather position, the feed-back shaft 150 will, by its part 150b, move the stop 165 into engagement with the plunger 117 of the underspeed governor so as to keep the ports 120 and 121 of the underspeed governor closed. That prevents leakage or drainage from the actuating chamber of the blade servomotor 33 thru the underspeed governor when the propeller is standing still for a period of time.

To unfeather, the pilots control lever 17 must be set within the governing range. If the pilots switch PF is then pulled right in Fig. 3, the pump motor 47 operates the pump 24 for unfeathering so long as the switch PF is held in right position, the underspeed governor 111 will then maintain fluid circuit connections until the unfeathering is complete; and then the actuator 13 and the coordinating unit is again under the control of the lever 17.

When starting on the ground, the control lever 17 is placed in the start position whereupon the coordinating unit 15 and the actuator 13 moves the regulator control arm 19 in the blade angle control range and adjusts the fuel of the turbine accordingly.

Electrical system The hydraulic regulator faithfully responds to control by the electrical system shown in Figs. 3 and 4 by which all of the controls are effected and unsafe propeller operations avoided.

Electric governor This system includes the control unit 10 (Figs. 3 and 4), a positioning actuator 13 (Fig. 3), and the alternator 8 (Fig. 3). The alternator is a three-phase generator bolted on to the turbine accessory mounting pad and geared to the turbine shaft and the propeller. Therefore, the voltage and frequency output of the alternator is directly proportional to the speed of the propeller. The voltage output of the alternator 8 is directed to the control unit 10 where it is matched with a constant voltage. When the alternator voltage is equal to the constant voltage an on-speed condition exists. Any variation in alternator voltage with respect to the constant voltage causes the solenoid valve 21 in the regulator 7 to be energized in the proper direction for rebalancing the system. Manipulation of the control lever 17 selects the desired governing speed thru the operation of the actuator 13 and the coordinating unit 15. The actuator determines the position of the regulator control arm 19 and also controls the circuits which set up the desired governing speed. This control of the solenoid valve 21 causes a pulsing or vibratory movement thereof during on-speed which manifest in a pulse ratio of unity, or 50:50, while a corrective impulse may be in the nature of 49:51, 60:40, :20, 10:90, etc., or vice versa, and in some instances may be in the ratio of 0:100 resulting in what is termed solid flow. One such system accomplishing the exact control of the solenoid valve 21 is that disclosed in the copending application Serial No. 94,984, filed May 24, 1949, now Patent No. 2,669,312.

Referring to Figs. 1 and 3, the control unit 10 contains the primary governing circuits by which a speed signal received from the alternator 8 is translated into the proper signal to the solenoid valve 21 to correct for offspeed, and by which selection the desired condition and regime of propeller operation is made. The actuator 13 is geared to drive three potentiometers 166, 166A and 1668, and to operate a bank A of limit switches in the proper sequence. The Potentiometer 166 is of 250 ohms and enters into selection of condition and regime of operation. Potentiometer 166A is of 500 ohms and operates as an immediate speed adjustment. Potentiometer 166B is of 5000 ohms and operates to determine the frequency of oscillator 0 having the function disclosed in Dinsmore et al. application Ser. No. 94,984, filed May 24, 1949, now Patent No. 2,669,312.

The 500 ohm potentiometer 166A in the actuator 13 and a variable resistor 168 in the control unit 10 form a bridge used to vary the speed signal from the alternator 8 so that a selected governing speed may be obtained. To trace this circuit through, three phase current emerges from the atlernator 8 and one phase passes through a rectifier and voltage regulator unit 169 (Fig. 3) which rectifies the A. C. output of a transformer to D. C., increases the voltage, and through the use of a choke coil and condensers, smoothes out the voltage to relatively pure D. C. This voltage is then connected to either side of a voltage regulator tube, which will maintain a constant voltage regardless of changes in turbine speed (changing alternator voltage) and thereby supply a constant voltage through wires 170, 171 across terminals 172 and 173 of a governor bridge BR (Fig. 4), and provides a constant voltage with which the speed signal from the alternator is matched as disclosed in the application referred to.

A phase of alternator voltage passes by wires 174, 175 through the resistive portion of the 500 ohm potentiometer 166A of the actuator 13. The slider of the potentiometer 166A in the actuator is connected with wire 178 so that a portion of the voltage passing through the potentiometer 166A is tapped off and passes through the primary coil of another transformer of a rectifier unit 179, where it is changed from A. C. to D. C., and smoothed out through the use of a choke coil and condensers. This voltage is then connected by wire 180 and by resistor 168 and wire 181 across terminals 182 and 183 of the governor bridge BR. Therefore the position of the slider of the potentiometer 166A determines the amount of the alternator voltage which is impressed across the primary of this transformer unit 179. The function of the variable resistor 168 will be described later.

A constant voltage is impressed across points 172 and 173 of the governor bridge circuit, and a voltage is impressed across points 182 and 183 which, for a given position of the potentiometer 166A, varies in direct relation to propeller speed. Since the governor bridge circuit BR is a double Wheatstone bridge, if the voltage across points 182. and 183 is equal to the constant voltage across the points 172, 173 then there will be no difference in voltage between points 184 and 185. If the voltage across points 182 and 183 is increased by, for example one volt, then a difference of /2 volt will exist across points 184 and 185. Using the midpoint 187 of the bridge circuit as a reference, point 185 assumes a potential of 4 volt and point 184 a potential of 4 volt. These equal and opposite polarities will increase or decrease in proportion to the D. C. voltage applied between points 182 and 183. Also, if the voltage applied to points 182 and 183 is decreased, then point 185 becomes more positive and point 184 more negative, the absolute value of the voltages still being proportional to change in voltage impressed across points 182 and 183. To sum this up, an increase in propeller speed with a consequent increase in alternator voltage will make point 185 more negative and point 184 more positive, while a decrease in propeller speed and alternator voltage will make point 184 more negative and point 185 more positive. These voltages are then used to control the circuit of solenoid valve 21.

If the voltage across the unregulated side 179 of the bridge circuit falls below the constant voltage side 169, an underspeed is indicated, and the solenoid valve 21 causes a decrease in pitch with a consequent increase in speed. The increase in speed raises the output of the alternator 8. The solenoid valve 21 will continue to increase propeller speed until the alternator voltage on the unregulated side 179 of the bridge equals the constant voltage on side 169. At this point an on-speed condition will exist and the solenoid valve 21 will then maintain that speed. Similarly, if the unregulated voltage on the bridge circuit is greater than the constant voltage, an overspeed is indicated and the solenoid valve 21 will cause an increase in pitch, thereby cutting down the output of alternator 8 until the voltages on the bridge circuit are matched.

If a variable resistor 168 is placed in the circuit on the unregulated side 179 of the bridge circuit, a controllable amount of the alternator output is dissipated through this resistor. Hence an increase in resistance will decrease the amount of alternator output applied to the unregulated side of the bridge and the solenoid valve will then cause an increase in propeller speed until the unregulated output again matches the constant voltage. Conversely, a decrease in resistance will cause the unregulated side of the bridge to have a higher voltage than the constant voltage and the solenoid valve will cause a decrease in propeller speed until equilibrium is again obtained. The resistive portion of resistor 168 to be included is determined by a motor M whose operation is effected by a discriminator D which compares the output or frequency from the alternator 8 delivered over the cable 9 with the selected frequency from an oscillator whose fixed frequency is controlled by the included resistive portion of the potentiometer 16613. The wiper or central contact of the potentiometer 166B is moved by the actuator 13 when it adjusts the regulator control arm 19, and the wipers of the potentiometers 166 and 166A. The movement of the wiper of potentiometer 166A is coordinated with movement of the wiper of potentiometer 166B since both are operated by the actuator 13. The function of potentiometers 166A and 16613 is to control the application of voltage for the alternator to the unit 179. Both potentiometers 166A and 16613 cooperate to control voltage at wires 180 and 181. In this way, the desired governing speed may be selected.

The position of the pilots control lever 17, which con trols the status of the actuator 13 and the 500 ohm potentiometer 166A, determines the amount of alternator output which is impressed on the primary of the transformer of unit 179. Since the secondary of this transformer in 179 leads to the unregulated side of the bridge circuit, the position of the pilots control lever 17 determines the speed at which governing occurs.

Since an ottspeed creates a difference in voltage across points 184 and 185 on the governor bridge, this voltage difference is used to control the solenoid valve circuit. Solenoid valve action is controlled through relay (PR) by a multivibrator circuit MV composed of two vacuum 9 tubes V1 and V2 that produce current pulses in plate circuits 188 and 189 whose relative duration can be varied by the respective grid voltages. These current pulses are out of phase with each other and the range of control is from a condition of steady current fiow from one plate and zero from the other, to a condition where the first plate current is zero and the second is a steady current flow. Between these two extremes, the current pulses occur with the ratio of the relative time duration of these pulses being constantly adjusted by the grid voltages.

Point 184 of the governor bridge is connected by wire 190 to the grid of tube V1 and point 185 of the governor bridge is connected to the grid of tube V2. Therefore, variations in propeller speed and alternator voltage cause corresponding variations in the grid voltages of the multivibrator tubes. This then causes a corresponding varia- .tion in the duration of the output pulses of the two tubes.

The pulsating efiect, when applied to the solenoid valve 21, causes jitter with the relative duration of the pulses, causing the valve to dwell longer on one side than the other to provide governing. The output (plate) circuits 188, 189 of the multivibrator tubes are connected to an amplifier section 192 in the usual manner and by the usual means, and thence by output circuits 193, 194 connected to windings 195, 196 of a pulsing relay PR.

A pulse on wire 194, enters the relay at terminal 197 and enerigizes the coil 196 whose circuit to the positive plate power supply is completed by wire 19S and terminal 199 to the power supply. A pulse from wire 193 cuergizes the coil of the pulsing relay through terminal 202. The circuit to the positive plate power supply is completed by the same path used for the relay coil 196. Thus a pulse from one tube will energize the relay coil 195 and a pulse from the other tube will energize the relay coil 196, the duration of energization of these relay coils being controlled by the duration of the pulse .eminating from the tubes V1 and V2. The electric current which is controled by this relay PR comes from a 28-volt supply wire 203 which is connected with terminal 204. When coil 195 is energized, a contact 260 electrically connected with terminal 204 moves into engagement with a contact 261 connected with wire 205. When coil 196 is energized, contact 260 engages a contact 271 connected with wire 206. The connections between wires 205 and 206 and the solenoid valve 21 are under control by a safety circuit to be described.

Actuator Whether the control signals appearing on lines 193, 194 (Fig. 4) are equal or unequal depends somewhat upon the status of the actuator 13. If the actuator is not operating, the signals from the governor 10 will be equal and opposite in effect when the engine is on-speed, or the signals will be unequal when correcting for an ofispeed. If the actuator is operating for the purpose of making some adjustment or change in the regime of propeller operation then the signals from 193, 194 will be unequal. As diagrammatically illustrated in Fig. 3, the actuator 13 has a motor 163 that controls the position of the regulator control arm 19 and actuates the movable contacts or slides of a bank of potentiometers 166, 166A and 166B. The motor 163 likewise causes the movement of cams that actuate a bank A of limit switches in a proper sequence. Motor field coil 241 is continuously energized.

The operation of motor 163 is controlled by circuit I, IIA, IIB, IIIA, IIIB (Fig. 5). In circuit I, there is a bridge circuit under control by pilot levers 17 and 17 (Fig. 3) which are used respectively for the control of two turbines which are mechanically connected with the same propeller. Either one or both of the turbines may be used to drive the propeller. In circuit I, there is a bridge circuit comprising potentiometers 1671) and 167d, the sliders 211 of which are respectively actuated by levers 17 and 17. Potentiometers 16712 and 167d are connected in parallel between the 28 volt D. C. wire 203 and ground. If lever 17 is set for greater power development than lever 17, the slider 211 of potentiometer 167d will be so located relative to slider 211 of potentiometer 16711 13 that current will flow in coil Pc of a polarized relay P in such direction as to cause its armature 212 to engage contact 214. If the lever 17 is set for greater power development than lever 17, current flow in coil Pc is reversed and the armature 212 of relay P engages contact 213. In either case, an actuator control bridge circuit is established with coil 209 of micro-positioner relay MP across the bridge. If armature 212 of relay P engages contact 214, the coil 209 of relay MP is connected between wiper 207 of potentiometer 166 and wiper 211 of potentiometer 1670. If armature 212 of relay P engages contact 213, the coil 209 of relay MP is connected between wiper 207 of potentiometer 166 and wiper 211 of potentiometer 167a. Circuit I provides means whereby control over motor 163 by lever 17 or 17' can be se lected. Circuit I provides means whereby the direction and extent of operation of motor 163 is determined by that one of the levers 17 or 17' which has control. For example, if lever 17 has control and it is moved in the direction to demand a lower governed speed and therefore a correspondingly higher blade pitch, the bridge circuit which includes potentiometers 166 and 167c is unbalanced and current flows in coil 209 of polarized relay MP in such direction that armature 219 of relay MP engages contact 220 and circuit IIA is established as follows: wire 203, armature 219, contact 220, high blade angle limit switch 223, wires 224 and 225, contacts 226 and 227 of feather limit relay FL (then deenergized), wire 228, coil IPc of increase pitch relay IP and ground. When coil IPc receives current, relay IP is energized and the circuit IIIB is established as follows: wire 203, contacts 229, 230 and contacts 231, 232 of relay IP, wire 233, armature of motor 163, wire 235, contacts 236, 237 and contacts 238, 239 of relay DP (then deenergized) and ground. Motor 163 turns wiper 207 of potentiometer 166 in a direction to balance the bridge circuit including potentiometers 166 and 1670. When the bridge is balanced, current flow in coil 209 of relay MP ceases, armature 219 is spring returned to neutral position out of engagement with contact 220, coil IPc is open-circuited, relay IP is deenergized, its contacts 229, 230 and contacts 231, 232 separate and motor 163 stops and it is mechanically disconnected from the mechanism which operates the wiper 207 of potentiometer 166 and which moves the lever 19 (Fig. 3), and motor of said mechanism is arrested by a brake. Coil 234 (Fig. 3), which is in series with the motor armature, receives current whenever the armature of motor 163 receives current. So long as coil 234 receives current, a clutch (not shown) is engaged to mechanically connect the motor armature with the mechanism which operates wiper 207 and lever 19 and the cams which operate the limit switches in bank A. When the armature of motor 163 is disconnected from wire 203, coil 234 is deenergized; and, by a spring not shown, the clutch is disengaged and a brake is applied to stop the mechanism so that there is no coasting thereof. If higher governed speed and correspondingly lower blade pitch is demanded by the control lever 17, current flows in coil 209 of relay MP in a direction to cause armature 219 to engage contact 221 and circuit HE is established as follows: wire 203, armature 219, contact 221, wire 242, low blade angle limit switch 243, and negative range limit switch 244, wire 245, contacts 246, 247 of feather limit relay FL (then deenergized), wire 248, contacts 249, 250 of relay IP (then deenergized), coil DPc of decrease pitch relay DP. Relay DP having been energized, circuit IIIA is established as follows: wire 203, contacts 251, 238 and contacts 237, 252 of relay DP, wire 235, armature of motor 163, wire 233, contacts 253, 231 and contacts 230, 254 of relay IP (then deenergized), wire 255, contacts 256, 257 of relay DP and ground 240. Coil 234 receives current to engage the clutch and to release the brake and motor 163 drives the actuator mechanism in the direction to move the wiper 207 in the direction to 14 balance the actuator control bridge including potentiameters 166 and 1670. When this bridge is balanced, current flow in coil 209 of relay MP ceases, armature 219 is spring returned to open position, coil DPc is opencircuited, relay DP is deenergized, circuit IIIA is opened,

motor 163 stops, the clutch is disengaged, the brake is applied and the mechanism stops.

The direction which motor 163 operates and the extent of its operation in either direction of its movement is determined by the direction in which wiper 211 of potentiometer 1670 is moved by the controlling lever 17 and by the extent of this movement in either direction of its movement. Wiper 207 of potentiometer 166 operated by motor 163 serves as a follow-up to discontinue the operation of the actuator 13 when the demand for its operation has been satisfied.

A function of motor 163 is to change the setting of the governor 10 either for governing at increased speed or for decrease speed, the setting being dependent on the direction of movement of the controlling lever 17 .from a previous position and on the extent of its movement. When increase in speed setting is demanded, motor 163 moves the wipers of potentiometers 166A and 166B in the direction to cause the speed setting of the governor to be increased. Since increase in governor speed setting will result in decrease in blade pitch, circuits IIB and IIIA which are completed for operation of motor 163 to increase governed speed setting are called decrease pitch circuits in Fig. 5. If decrease in speed setting is demaned, motor 163 is operated in consequence of completion of circuits HA and IIIB to move the wipers of potentiometers 166A and 166B in the direction to cause the speed setting of the governor to be decreased. Circuits IIA and IIIB are called increased pitch circuits r because the governor causes pitch to be increased when governor speed setting is decreased.

Limit switch 223 of bank A in circuit IIA opens when blade angle is the highest value permitted in the governing range. Limit switch 243 of bank A in circuit IIB opens when blade angle is the lowest value permitted in the governing range. Limit switch 244 of bank A in circuit IIB opens when blade angle is at the greatest allowable negative value. As will be explained later, switch 243 is by-passed when blade angle in a low positive range and in a negative range without governor control is desired and relay MP and switch 223 are bypassed when feathering is desired.

The governing range of operation of motor 163 is limited by virtue of the stop a (Fig. 2) which is received by a notch 19b in a ring 19a to which lever 19, operated by motor 163, is attached. Motor 163 cannot operate further in either direction to increase or decrease governor speed setting than permitted by the notch 19b,

the ends of which receive the stop 160a.

As stated before, the governor 10 operates to cause the oppositely acting solenoids 75 and 76 of valve 21 (Fig. 2) alternately to receive electrical pulses which are equal in duration when the engine is on speed and which are unequal in duration in order to cause valve 21 to correct a deviation from governed speed. In case of failure of the electronic governor 10 to function properly, a safety device operates automatically to disconnect it from the solenoid valve 21 which automatically moves to port closing position so that there is no disturbance of control hydraulically by the over-speed and underspeed governors or by the blade angle control which can be eifected manually by operating lever 19 in Fig. 2.

Safety circuit When the governor 10 is operating to maintain a speed for which it has been set to control, the pulsing relay PR alternately completes circuits IVA and IVB (Fig. 5). Circuit IVA includes D. C. source wire 203, contacts 260 and 271 of relay PR, wire 206, contacts 272 and 273 of relay IS when energized, Wires 274', 274, contacts 275 and 276 of governor disconnect relay GD (when not energized), wire 277, contacts 278 and 279 of governor transfer relay GT (when not energized), slip ring and brush a, wire 94, contacts 87 and 81 of centrifugal switch CS (closed above a certain low propeller speed as 250 R. P. M.), a decrease pitch solenoid 75 and ground return 77 to the current source. A form of centrifugal switch CS is shown in copending application, Serial No. 202,612, filed December 26, 1950, now Patent No. 2,699,304. Circuit IVB includes D. C. source wire 203, contacts 260 and 261 of relay PR, wire 205, contacts 262 and 283 of relay DS when energized, wires 284 and 285, contacts 266 and 267 of relay GD, wire 268, contacts 269 and 270 of relay GT, slip ring and brush 20a, wire 93, contacts 86 and 80 of switch CS, increase pitch solenoid 76 and ground return 77 to the current source. The described contacts of relays GD and GT and centrifugal switch CS remain closed when the controlling lever 17 is in the governor control range. Therefore the pulsing circuits IVA and IVB are operative provided relays IS and DS remain energized. For each of these relays there is an energization initiating circuit and an energization maintaining circuit. Circuit V is the energization initiating circuit of coil DSc of relay DS.

Assume that contacts 260, 271 of relay PR close first when the governor 10 begins operation. The following circuit V in Fig. 5 is established: Wire 203, contacts 260 and 271, wire 206, contacts 272 and 272a of relay IS (initially deenergized), coil DSc of relay DS and capacitor C2 in parallel, Wire 274, solenoid 75 and ground. This first pulse of current energizes relay DS and charges capacitor C2. The resistance of coil D56 is 80 to 90 times that of solenoid 75. Most of the voltage drop in this initial circuit occurs across coil D80 and the capacitor C2 in parallel which is charged by this first pulse of current. The small current which flows through solenoids 75 during the first pulse is not large enough to move plunger 63 of valve 21 appreciably against the action of the centering spring. When contacts 260 and 271 of relay PR open and the first pulse of current is interrupted, capacitor C2 discharges and its discharging current flowing through coil DSc creates an electromagnetic field in the relay structure and a magnetic force on the movable contact arm which holds the relay DS contacts closed during the normal time interval required for one complete cycle of the pulsing relay PR until contacts 260 and 271 close again.

Contacts 262 and 283 of relay DS in circuit IVB were closed when this relay was energized on the first pulse and are held closed by the flow of discharge current from capacitor C2 through the coil DSc. When contact 260 of relay PR engages contact 261 to complete circuit IVB, the second pulse of current flows through these contacts, wire 205, contacts 262 and 283 of relay DS, wire 284, wire 285, contacts 266 and 267 to solenoid 76. This pulse of current is much stronger than the first pulse because it does not flow through a safety circuit relay coil D80 or 180 whose resistance is 80-90 times that of the solenoid 75 or 76 and it does not charge a capacitor C1 or C2. This pulse of current is strong enough to move plunger 63 of valve 21 in the normal manner. When this second pulse of current is interrupted by the opening of the contacts 260 and 261, the larger electromagnetic field surrounding the solenoid 76 collapses inducing a voltage which causes current to continue to flow through the solenoid 76 in the same direction as it did before the contacts 260 and 261 opened. As shown in circuit VIII a closed circuit, through which this induced voltage can cause current to flow, exists towards the ground of solenoid 76 through the common ground to rectifier R1 to coil 18c and capacitor C1 in parallel and thence through wire 285 to the other end of solenoid 76.

This sudden surge of current caused by the collapse of the electromagnetic field surrounding the solenoid 76 charges the capacitor C1 and flows through coil ISc energizing it and holding relay IS closed. After the electromagnetic field surrounding the solenoid 76 has completely collapsed and no voltage is being induced in solenoid 76 and no current supplied at that instant by its flowing through the coil ISc, capacitor C1 discharges. The discharging current of capacitor C1 flows from one side of capacitor C1 to the other through the coil ISc. The electromagnetic field induced in the relay structure by the current flowing through its coil ISc creates a magnetic force on the movable contact arm which holds the contacts of relay 150 closed during the normal time interval required for one complete cycle of the relay PR. The hold in time of the Be relay after each pulse can be adjusted by varying the resistance of the coil 18c and the capacitance of the capacitor C1.

The third pulse occurs when contacts 260 and 271 close again to complete circuit IVA. Current flows out wire 206, through contacts 272 and 273 of relay IS which was energized when contacts 260 and 271 opened at the end of the second pulse, through wire 274', wire 274, contacts 275 and 276 to solenoid 75. This pulse of current to solenoid 75 is much larger than the first pulse because it does not flow through a safety circuit coil DSc whose resistance is 80 to times that of solenoid 75 and it does not charge capacitor C2. This pulse of current is strong enough to move plunger 63 of valve 21 in the normal manner. When this stronger current is interrupted by the opening of contacts 260 and 271, the electromagnetic field surrounding solenoid 75 collapses inducing a voltage which causes current to flow through solenoid 75 in the same direction as it did before contacts 260 and 271 opened. As shown in circuit VI, a closed circuit through which this induced voltage can cause current to flow, exists toward the ground of solenoid 75, through the common ground to rectifier R2 to coil D80 and capacitor C2 in parallel, through wire 274, to the other end of solenoid 75. This sudden surge of current caused by the collapse of the electromagnetic field surrounding solenoid 75 charges capacitor C2 and flows through coil DSc energizing it and holding relay DS closed. After the electromagnetic field surrounding solenoid 75 has completely collapsed and no voltage is being induced in solenoid 75 and no current supplied at that instant by its flowing through the coil DSc, capacitor C2 discharges. The discharging current of capacitor C2 flows from one side of capacitor C2 to the other through coil DSc. The electromagnetic field induced in the relay structure by the current flowing through its coil DSc creates a magnetic force which holds the contacts of relay DSc closed during the normal time interval required for one complete cycle of relay PR. The hold in time of the DSc relay after each pulse can be adjusted by varying the resistance of the coil D50 and the capacitance of the capacitor C2.

The safety circuit is now in normal operation. Each pulse goes directly to the solenoid 75 or 76. The inductive kick or surge :of current as each pulse is interrupted charges the capacitors C1 and C2 and their discharge current through their respective relay coils 18c and DSc holds each relay energized until the cycle repeats.

If contact 260 had initially first engaged contact 261 when the governor 10 began to operate, circuit VII for initiating energization of relay IS would have been completed as follows: wire 203, contacts 260 and 261 of relay PR, wire 205, contacts 262, 263 of relay DS (then de-energized), wire 264, coil 18c and capacitor C1 in parallel, wire 285, solenoid 76 and ground. This pulse of current would energize relay IS and charge capacitor C1 but would not have enough strength to move plunger 63 of valve 21 appreciably against its centering spring. The small electromagnetic field surrounding solenoid 76 does not generate an appreciable voltage as it collapses when contacts 260 and 261 separate. Capacitor C1 dis- 17 charges after these contacts open and its discharging current flowing through coil ISc holds this relay energized for longer than the time required for one cycle of the pulsing relay PR. The next pulse would occur when contacts 260 and 271 made and current flowed through wire 206, contacts 272 and 273 of relay IS that was energized on the first pulse and held closed by the discharge current of capacitor C1, through wire 274 to solenoid 75 as shown in circuit IVA. This strong pulse of current which does not have to overcome the impedance of the relay coils (iSc or DSc) and their associated capacitors (C1 or C2) is interrupted when contacts 260 and 271 of relay PR open. The electromagnetic field surrounding solenoid 75 collapses and generates a surge of current tending to flow in the same direction as before the contacts opened, as shown in circuit VI, through solenoid 75 towards ground through rectifier R2, relay coil DSc and capacitor C2 in parallel to the other end of solenoid 75. The surge of current energizes relay coil DSc and chargescapacitor C2. Capacitor C2 discharge current flowing through the relay coil DSc holds this relay energized during the time interval required for the cycle to repeat. Thethird pulse would start when contacts 260 and 261' closed again completing circuit IVB through wire 205, contacts 262 and 283, wire 284 to solenoid 76. When contacts 260 and 261 of the relay PR open, the electromagnetic field surrounding coil 76 collapses generating a voltage which tends to cause the current to continue flowing through solenoid 76 in the same direction as it was before the contacts opened. This surge current flows through solenoid 76 to ground to rectifier R1 to coil 18c and capacitor Cl'in parallel, through Wire 2351' to the other end of solenoid 76 as shown in circuit VIII. This surge of current energizes relay ISc and charges capacitor C1. Capacitor C1 discharge current flowing through relay coil ISc holds this relay energized during the time interval required for the cycle to repeat. The safety circuit would now be in normal operation. Each pulse would go directly to its respective solenoid 75 or 76. The inductive kick or surge of current as each pulse is interrupted charges the capacitors Cl. and C2 and their discharge current through their respective relay coils 18c and D80 holds each relay energized until the cycle repeats.

From the foregoing it is apparent that the maintenance of the solenoid pulsing circuits during the governing regime is dependent upon maintenance of energization of relay IS and DS. Energization of relay IS whose contacts 2'72 and 273 are in circuit IVA depends on the pulsing of solenoid 76 in circuit IVB. Energization of relay 138 whose contacts 262 and 283 are in circuit IVB depends on the pulsing of solenoid 75 in circuit IVA. If solenoid '76 does not receive a pulse, relay IS becomes deerrergized and solenoid 75 cannot receive a pulse. If solenoid 75 does not receive a pulse, relay DS is deenergized and solenoid 76 does not receive a pulse. If pulse failure be only momentary in duration, for example, omission of two or three pulses, the relays DS and IS remain energized. If pulse failure is a permanent condition due to failure of the governor to function properly or to a loose connection anywhere up to the solenoids 75-, 76, the safety relays IS and DS disconnect the governor from the solenoids 75-76 and control of blade angle is taken over by the hydraulic system which prevents overspeeding and underspeeding by blade angle control as described.

Means are provided for over-riding the safety circuits when a change in governor setting is taking place. This is necessary because, during said change, one of the solenoids 75, 76 is continuously energized to cause what is known as a solid of hydraulic fluid to the blade angle servo 33 (Fig. 2). Change in governor setting requires operation of motor 163 in one direction or the other. To effect motor operation, either the wire 233 is positive in polarity While wire 235 is negative or vice versa. In

etiher case as shown in circuit IX, current will flow from wire 233 through rectifier R5 or from wire 235 through rectifier R6 to wire 291 and thence through'parallel circuits which are as follows: rectifier R3, wire 292, contacts 294, 295 of relay IS (still energized), wire 264, coil ISc, wire 285, solenoid 76 and ground; and rectifier R4, wire 293,'contacts 296, 297 of relay DS (still energized), coil DSc wire 274, solenoid 75 and ground. Therefore relays IS and DS remain energized While the governor setting is being changed. After the change in governor setting has been completed,'wires 233 or 235 carry no current and wires 292 and 293 receive no current. Therefore the safety relays IS and DS depend thereafter for their energization upon the pulsing of the solenoids 75 and 76 while the governor is operating to maintain a selected speed.

Feathering Feathering may be accomplished at any time from either the blade angle control range or the governing range by merely pushing in the feathering button 164. All shutdowns, both normal and emergency, are made by this one operation, and no other levers or switches need be touched. When the feathering button 164 is pushed in, the propeller goes to feather, the fuel is automatically shut oif, and the gear box clutches in the transmission from the two turbines to the propeller are automatically disengaged. This may be done by either the pilots feathering control switch PF or the engineers feathering control switch EF.

When the pilots control PF is pushed inwardly, the member 164 connects the D. C. source Wire 203 connected with contact 300 with contacts 302, 301 and 303 to establish circuits X, XIII and XV, respectively. When contacts 300 and 302 are connected, circuit X is established. Referring to circuit X, the member 164 connects D. C. voltage as follows: D. C. source wire 203, contacts 30%, 164 and 302, wire 304, time delay switch TD, contacts 306, 307 of relay BB (then deenergized), wire 334, coil Me of relay M and ground. A solenoid BB is connected in parallel with relay coil M0. The function of solenoid BE is to hold contact 164 in switch closing position shown in circuits X, XIII and XV. The func tion of time delay switch TD is to maintain energization of coil Me and solenoid BE for time ample for feathermg. switch contact 164 in circuit closing position for feathering. Relay coil CCc also receives current from contact 302 and, when energized, closes contacts 308 and 309. A control circuit for the actuator motor is thereby established as shown in circuit XI which includes contacts 335 and 338 of relay M (then energized), contacts 308 and 309 of relay CC (then energized), wire 310, contacts 226 and 227 of feather limit relay FL (then deenergized), wire 228 and coil IPc of relay IP and ground. Circuit XI therefore energizes the coil IPc of increase pitch relay IP independently of the micropositioner MP and independently of the limit switch 223. Relay coil IPc being energized, circuit XII is completed as follows: current source wire 203, closed contacts 229, 230 and 231, 232 of relay IP, wire 233, armature of motor 163, wire 235, contacts 236, 237 and contacts 238, 239 of relay DP (then deenergized) and ground. This causes the motor 163 to operate in the increase pitch direction for operation of the regulator lever 19. At the end of the time interval which is ample for feathering, switch TD opens automatically and relay coil Mo and solenoid BE are opencircuited and a spring returns contact 164 to open position.

Circuit XIII, established by engagement of contact 164 with contacts 300 and 301, includes source wire 203, wire 321, coil GTc of the governor transfer relay and ground. Relay GT, when energized, disconnects the signal transfer leads 266, 267 from the wires 93 and 94 and connects wires 92, 93, 94 with a current source 320 included in cable 326 (Fig. 4) substantially as shown in cir- Therefore, the pilot is not required to hold the cuit XIV. Therefore, any signal energy developed by the electric governor 10 and applied through the pulses relay PR has no effect upon the fluid pressure circuit within the regulator of the propeller. That is necessary since operation of the actuator motor 163 directly that it starts to rotate moves the wiper 207 of the potentiometer 166 effecting an unbalance of the control bridge through the coils 209 of the micropositioner MP and the potentiometer 167. This unbalance is in such a sense that if the governor were allowed to function it would tend to prevent pitch change in the proper direction, hence the effect of the governor is entirely cut off by transfer of the connections by the energization of the governor transfer relay GT. When relay GT is energized, the current source 320, characterized by 200 volts, 3-phase, 400 cycle A. C., is connected to wires 93, 94 and 92 respectively by closure of pairs of contacts 325, 270 and 323, 279 and 324, 322 as shown in circuit XIV. Wire 92 is connected with electric motor 47. Contacts 86, 89 and 87, 90 of a centrifugal switch CS, when closed, connect wires 93 and 94 with electric motor 47. The first portion of the feathering operation will be accomplished by the supply of fluid pressure of the system pump 22 and the additional pump 23 Within the regulator of the rotating propeller. Immediately as the feathering shift begins, a decrease of propeller rotation takes place; and, since the pumps 22 and 23 are operated only upon propeller rotation, their pressure output decreases as the speed decreases and the flow and pressure of fluid within the trunk line 28 will decrease such as to allow the flow control valve 57 to connect the output of pump 24 with the trunk line 28. At some value of decreased R. P. M., the centrifugal switch CS will have switched the connections on wires 93 and 94 from the solenoid valve connections 80 and 81 to the feathering motor connections 89 and 90. In any event, if there is insuflicient fluid pressure within the hydraulic system to complete the feathering shift, the motor driven feathering pump 24 will be energized and its output connected with the trunk line 28 to complete the feathering operation. In case the propeller is not rotating, the feathering position may be effected by operation of the feathering pump 24 without the assistance of pumps 22 and 23.

When the pilots feathering control PF is pushed inward or left in Fig. 3, circuit XV is completed as follows: current source wire 203, contacts 300, 164, 303, wire 311, coil Sc of relay S and ground. Energization of relay S establishes circuit XIX which includes wire 203, closed contacts 312 and 313 and wire 16 which leads to the fuel control valve (not shown), thereby properly reducing the fuel to the turbine to adjust the turbine for power and speed suitable to feathering of the propeller. When relay S is energized, contacts 314 and 315 are closed to establish circuit XVI which includes wire 203, wire 316, coil GDc of governor disconnect relay GD and ground and contacts 317 and 318 of feather limit relay FL (deenergized), wire 319, solenoid AA and ground. The contacts controlled by relay GD are shown in circuits IVA and IVB. When relay GD is energized, the signal control lines 268 and 277 are entirely disconnected from any signals that may come from the governor 10 by way of wires 205 or 206. At the same time the solenoid AA withdraws the plunger 160a which permits the actuator motor to move the regulator control arm 19 out of the governing range into the feathering range. The regulator control arm 19 thereby actuates through shaft 144 (Fig. 2) to shift the cam plate 145 of a selector control valve 138 and the floating arm 148 of the distributing valve 137. The selector control valve 138 now switches in the distributor valve 107 in place of the overspeed and underspeed valve and the increased pitch port of the distributor valve 107 is opened wide to the increase pitch chamber 74 of the blade servomotor 33. The actuator motor 163 continues to run until the blades reach the feathered position whereupon the feather limit 20 switch 327 closes and establishes circuit XVII which includes wire 203, wire 328, coil FLc of the feather limit relay FL and ground. When relay FL is energized, contacts 226, 227 of circuit XI open and coil IPc is opencircuited and circuit XII is interrupted and the motor 163 stops.

Upon the completion of feathering which is marked by the energization of coil FLc of the feather limit relay FL, its contacts 317 and 318 open to deenergize the solenoid AA which had retracted stop 160a (Fig. 2). A spring urges stop 160a (Fig. 2) against ring 19a preparatory to being received by notch 1% when lever 19 is returned to a position in the governing range by the uir feathering operation to be described. Contacts 226 and 227 (circuit XI) are opened to deenergize increase pitch relay I? and contacts 246, 247 (circuit IIB) are opened to prevent energization of coil DPc of relay DP preparatory to unfeathering. When the coil FLc of feathering limit relay FL is closed, current XVIII is established which includes wire 203, contacts 329 and 330, wires 331 and 311, coil Sc of relay S and ground. This maintains energization of relay S independent of circuit XV and circuit XIX is maintained for keeping the fuel valve closed. Energization of coil FLc of relay FL completes circuit XX which includes closed contacts 332 and 317 of relay FL and coil GDc of governor disconnect relay GI) and ground. Therefore, the governor is kept disconnected from the solenoid valve.

When relay M is energized, as shown in circuit XXII, wire 203 is connected by its closed contacts 335, 338 with wire 304 of circuit X, by its closed contacts 336, 339 with wire 321 of circuit XIII, by its closed contacts 337, 340 and wire 311 of circuit XV thereby by-passing the connected contacts of switch PF.

Feathering by the engineers feather control switch EF is effected by engagement of switch EF with contact 333 which connects wire 203 with wires 304a and 304 in circuit XXI. Therefore the same instruments are connected with wire 203 as in circuit X. Relay M being energized, wire 203 is connected with wires 304, 321 and 311 so that the functions of circuits X to XX will be performed as in the case of feathering by the pilots feather control switch PF.

Unfeathering Unfeathering of the propeller is accomplished either by the pilots feathering control switch PF being pulled outward or by movement of the engineers feathering switch EF being moved downwardly which establish circuits XXIII-XXVII, generally indicated in Fig. 7. At the conclusion of feathering, the feather limit switch 327 of bank A is closed and coil FLc of the feather limit relay FL is energized which effects energization of relays S and GD. The electric governor is therefore disconnected from the solenoid valve. The fuel to the turbine is also reduced or closed ofi, and the energizing circuit to the actuating motor is open. Energization of the feather limit relay FL has also deenergized increased pitch relay IP through open contacts 226 and 227. When the pilots switch PF is pulled right in Fig. 3, circuit XXIII is established as follows: wire 203, terminal 300, wire 301, contacts 342, 164, 301, terminal 301, wire 321, coil GTc of relay GT and ground; and circuit XXIV is established as follows: wire 203, terminal 300, Wire 341, contacts 324, 164, 343, wire 344, switch 217 of bank T coil UFc of relay UP and ground. Therefore circuit XIV is established and contacts 279 and 270 in circuits IVA and IVB are opened. Therefore the circuit connections from the electric governor to the solenoid valve are switched over to disconnect them and to supply energy from source 320 to the motor 47 of the feathering pump. When the propeller is feathered, the propeller is not rotating and hence the pump 22 and 23 are not supplying any fluid pressure. Therefore fluid under pressure is provided by the pump 24 when the feathering pump motor 21 47 is energized and when the flow control valve 57 is in position to connect the output of pump 24 to the pump line 28.

Circuit XXIV which had been established as described includes coil BBc of relay BB and ground. The energization of relay BB opens contacts 306 and 307 which disconnects the time delay relay TD and the feathering switch holding coil BE along with the coil Mc of relay M. Hence, there is no automatic time control set up for the completion of unfeathering and the contact 164- of pilots control switch PF mustbe held out against the contacts 301' and343 until unfeathering has been accomplished. When relay coil UFc in circuit XXIV is energized contacts 347 and 348 in circuit XXV are closed which provides a by-pass around contacts 246, 247 of relay FL so that the decrease pitch relay DP can be energized to complete the actuatormotor circuit substantially as shown in circuits XXVI and IIIA, to operate the motor 163 in a decrease pitch sense. Wh'enthe unfeathering operation is started the actuator motor 163 will have moved the wiper 2070f potentiometer 166 which unbalances the control bridge including the coils 209 of relay MP and wipers 211 of potentiometer 167. Therefore contacts 219 and 217 of relay MP close. (See circuits IIB and XXV.) Circuit XXV for energizing decrease pitch relay DP now includes wire 203, contacts 219 and 221 of the micropositioner MP, wire 242, low blade angle limit switch 243 (now closed), negative limit switch 244 of the actuator group A, wire 245, contacts 347 and 348 of unfeathering relay UF (now energized), contacts 249, 250 of relay IP (deenergized), coil DPc of decrease pitch relay DP, and ground. Closing of contacts 347, 348 of relay UF by-passes the open contacts 246, 247 of feather limit relay FL which is now energized. Decrease pitch relay DP being energized, closes contacts 251, 238 and 252, 237 as well as 256, 257 which establishes a running circuit XXV for the actuator motor 163. This running circuit is substantially identical with circuit IIIA earlier described.

The actuator motor 163 operates in a pitch decreasing direction to move the potentiometers 166, 166A, 1663 and the regulator control arm 19, and to cause opening of feather limit switch 327 and to cause closure of the high blade angle limit switch 233 of gang A. Movement of regulator control 19 in its return 'movement toward the governing range shifts the floating lever 148 of the distributor valve 137 and moves the valve plunger thereof to such position that the pressure source from trunk line 28 is directed to the decrease pitch chamber 73 of the blade actuating servo 33. At the start of the feathering operation, the selector valve 107 is still connecting the distributor valve 137 with the blade actuating servo and has disconnected the governing control by overspeed governor 95 and the underspeed governor 111. As soon as the blades are moved out of the feather position to an appropriate angle windmilling of the propeller will take place and rotate the propeller. Eventually, the pumps 22 and 23 will supply enough pressure and flow in pump line 28 to supply the demand in completing the unfeathering change. When that occurs, the flow control valve 57 will return the output of feathering pump 24 to the reservoir by way of the sump 51. By the time that the blades reach the governing range feather limit switch 327 of the actuator group A will have been opened to deenergize feather limit relay FL. Deenergization of feather limit relay FL permits contacts 246, 257 to close maintaining the decrease pitch circuit IIB. When relay FL is deenergized, contacts 226, 227 are closed such that the increased pitch circuit through the micropositioner MP is established substantially as shown in circuit IIA except that 219 and 221 of relay MP are closed which leaves relay IP deenergized. Contacts 246, 247 of the relay FP are closed which establishes a closed circuit through decrease pitch relay DP as substantially as shown incircuit IIB, the contacts 219 and 221 of MP being 22 closed.- Contacts 217, 218 of relay FL are closed which would normally energize the pitch stop solenoid AA shown in circuit XVI, however the relay S is deenergized and hence contacts 314, 315 are open which also permits the energization of the governor disconnect relay GD. Therefore the governor is connected to the solenoid valve and the pitch A is released to drop into the notch 19b when the regulator control arm 19 is moved back to a position within the governing range. The propeller having been returned to the governing range by unfeathering, the setting of the governor is established by circuit I; and, thereafter, differential pulsing by the electric governor 10 continues for circuits IVA and IVB.

Unfeathering by the engineers feathering switch EF effects the same result, and is schematically shown by circuit XXVH which incorporates switch member 347 of engineers feathering switch EF connected to wire 321 in place of the pilots feathering control circuit XXIII, and substitutes the contact 348 of the engineers feather control switch EF for the pilots control switch PF connected with wire 344 in circuit XXIV.

Blade angle control range for negative thrust The pilots lever 17 may be used to select the governing speed between the limits defined by the low blade angle limit switch 243 and the high blade angle switch 223 of the actuator gang switch A, and also may be used to select any blade angle between that defined by the low blade angle limit switch 243 and extending to the maximum negative angle defined by the negative range limit switch 244 of the actuator gang A. The control effected by the pilots lever 17 in connection with selecting a governor speed has been described with respect to circuits 1 to IX inclusive. There is no provision for feathering operation of the propeller by use of the pilots control lever 17 since it is unable to withdraw the blade angle stop 160a at the high pitch end of the governing range. In selecting a blade angle below the governing range the lever 17 is moved clockwise as shown in Fig. 3, which by its linkage 1672 and 167], moves the contacts 216, 217, 218 to the right, so that contacts 216, 218 engage contacts 349 and 350 respectively. At the same time, the control bridge through the micropositioner MP is unbalanced. The unbalance of the bridge through the relay MP sets up a control circuit according to circuit IIB energizing the decrease pitch relay DP, and the actuating motor 163 is operated in decrease pitch direction. The specific circuit for the governor disconnect is shown by circuit XXVIll while the energization of the decrease pitch relay is shown in circuit XXIX. By closing the switch contacts 216 and 349 of gang switch T, the current wire 203 is connected to wire 316 (circuit XXVIII) which leads to the coil DGc of the governor disconnect relay GD and thence to ground. A branch from 316 is through contacts 317, 318 of feather limit relay FL (deenergized) and thence through wire 319 and stop solenoid coil AA to ground. When relay GD is energized, the contacts 275, 276, 266, 267 of relay GD and shown in circuits IVA and IVB are open. When solenoid AA is energized the stop plunger 160a is withdrawn, permitting the regulator control arm 19 to be moved out of the governor control range. Movement of the pilots control lever 17 outside of the governing range also closes contacts 218 and 350 of the gang T, whereby the source Wire 203 is connected by contacts 219 and 221 of micropositioner MP, wire 242, Wire 352, contacts 350 and 218 of gang T, thence by wire 351 to negative range limit switch 244 to energize decrease pitch relay coil DPc as shown in circuit IIB. It should be noted that the connection between wires 352 and 351 provided by the closed contacts 218 and 350 of gang switch T by-passes the lower blade angle limit switch 243 of the actuator gang A, which switch 243 is opened upon passing beyond the low blade angle of the governing range. With the decrease pitch relay DP energized, the actuator motor circuit IIIA for the decrease pitch change is established. As soon as the actuator motor runs beyond the point of low blade angle limit switch 243, the regulator control arm 19 is operated to shift the distributor valve 137 in a direction to call for decrease pitch, and the selector valve is also shifted to substitute control by the distributor valve in place of the overspeed governor valve and the underspeed governor valve. In case the pilots lever 17 is moved to a small positive angle below the governing range, the shift of the blade 5 in moving to that angle will operate by its feed back 150 to restore the closed condition of the distributor valve 137 as has been explained heretofore. In case the pilots control lever 17 is moved to extreme clockwise position with respect to Fig. 3, the maximum negative thrust blade angle will be called for and the actuator motor 163 will continue to operate until the negative range limit switch 2. 4 is opened which deenergizes the decrease relay Di and stops the actuator motor 163. Generally the action in response to moving the pilots control lever 17 to any point below the minimum angle of the governing range operates the actuator 163 and regulator control arm l; to shift the plunger of distributor valve 137, this position calling for a specific angle. When the blade 5 is shifted to that selected angle, the feed back 150, acting upon the floating lever 148, restores the distributor valve 137 to the closed position, cutting off all further flow to the blade operating servomotor 33.

Return from negative thrust The shifting from negative thrust operation to the positive thrust or to the governing range is accomplished by the pilots control lever 17 being moved in counterclockwise direction as shown in Fig. 3. That movement of the lever 17 operates upon the gang of switches T to open contacts 216, 349 and contacts 218, 350 while contacts 217, 345 are closed. Movement of the lever 17 also operates upon the wipers 211 of the potentiometer 167 and effects an unbalance of the control bridge illustrated in circuit I. This unbalance is such as to cause current to flow through the coil 209 of the micropositioner MP and effect energization of the increase pitch relay 1? as indicated in circuit IIA. Eenergization of relay 1? causes the actuating motor 163 to operate in the increased pitch direction for shifting the potentiometer 166, for actuating the regulator control arm 19 and for sequentially closing the negative range switch 244 and low blade angle limit switch 243. This counterclockwise rotation of pilots lever 17 in moving the contacts of switch T does not establish any new circuits but merely restores circuit conditions that may be made use of in other controls of propeller operation all of which have been explained heretofore. The closing of contacts 217 and 345 of gang T connects relay BB and relay UF in parallel and to ground preparatory to being energized from the current wire 203 by either the pilots feathering switch PF or the engineers feathering switch EF. Thus the movement of the pilots control lever 17 to a point within the governing range depends upon the circuit relations illustrated in circuits I to IX inclusive, as illustrated in Fig. 5.

Propeller adjustment when propeller not rotating.-

Control of static propeller Control of the propeller blade angle while the propeller is not rotating and the craft is on the ground is effected by the feathering control switches PF and EF, their movement being in either a feathering or unfeathering direction. Normally the propeller blades would :be in the feathered position when the propeller is under the stated condition, and it is desirable to shift the blades to a position with least possible air resistance to rotation as in the instance of starting the turbine on the ground. By moving either the pilots feathering switch PF or engineers feathering switch EF to the unfeathed position will establish circuits contemplated from X to XXIII to XXVI. The propeller being at rest or not rotating,

the centrifugal switch CS will be shifted to a position for connecting the feathering pump motor 47 with the current source 320, and the governor transfer relay GT upon closure of contacts 842 to 341' or 347 of switch EP will be energized substantially as indicated by circuits XIII and XIV. Hence fluid pressure will be supplied to the pump line 28 for supply to the distributor valve 137 which will have been shifted by the actuator motor 163 and the regulator arm 19 to call for the decrease pitch shift distribution of pressure fluid to blade angle servo 33. The control of the actuator motor circuit will be established in accordance with the description of circuits XXV and XXVI. Therefore the blades of the propeller are shifted to any desired lesser angle by manipulation of the feathered control switches into the unfeathcred position. An increase angle of the setting of the propeller blades is accomplished by manipulation of the feathered control switch PF and EF to the feathering pitch position. The circuits thereby established will follow those described with respect to circuits X to XXII.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. The combination with blade angle control means for variable pitch propellers having a fluid pressure source, pressure actuated means for changing the angle of the propeller blades, propeller borne governing means for limiting the high pitch and low pitch angles, and an oscillatable valve connected with the pressure source for directing the fluid thereof to the pressure actuated means for increasing and decreasing the blade pitch, of electromagnetic means for operating the said oscillatable valve and including a pulsing relay having electrical connection with said electromagnetic means, a pair a safety relays each including an energizing coil and normally closed contacts for completing the electrical connections between the pulsing relay and said electromagnetic means, means connecting the normally closed contacts of each safety relay in series with the coil of the other safety relay for initially interrupting said normally closed contacts of the said other safety relay and for closing a pair of normally open contacts of said other relay, and means connecting the energizing coils of said safety relays with said electromagnetic means so that the current induced by periodic energization and deenergization of the said electromagnetic means maintains energization of the energizing coils of both safety relays whereby any failure in the operation of said pulsing relay will interrupt the electrical connections between said pulsing relay and said electromagnetic means.

2. The combination with blade angle control means for variable pitch propellers having a fluid pressure source, pressure actuated means for changing the angle of the propeller blades, propeller borne governing means for limiting the high pitch and low pitch angles, and an oscillatable valve connected with the pressure source for directing the fluid thereof to the pressure actuated means for increasing and decreasing the blade pitch, of electromagnetic means for operating the said oscillatable valve and including a pulsing relay, a pair of control circuits connecting the pulsing relay with the electromagnetic means and adapted for selective energization by said pulsing relay, a safety relay for each control circuit having a pair of normally closed contacts and an energizing coil, means serially connecting the said normally closed contacts of each safety relay with the energizing coil of the other safety relay for initially completing the control circuits when the respective safety relay is deenergized, conductor means including normally open contacts in each safety relay for completing one of said control circuits around the energizing coil of the other safety relay when the coil of said each relay is energized, and means connecting the energizing coils of said safety relays with said electromagnetic means so that the current induced by periodic energization and deenergization of the said electromagnetic means maintains energization of the energizing coils of both safety relays whereby any failure in the operation of said pulsing relay will interrupt the electrical connections between said pulsing relay and said electromagnetic means.

3. The combination with blade angle control means for variable pitch propellers having a fluid pressure source, pressure actuated means for changing the angle of the propeller blades, propeller borne governing means for limiting the high pitch and low pitch angles, and an oscillatable valve connected With the pressure source for directing the fluid thereof to the pressure actuated means for increasing and decreasing the blade pitch, of electromagnetic means for operating the said oscillatable valve and including a pulsing relay providing a succession of control pulses, a control circuit connecting the pulsing relay with the electromagnetic means and adapted for pulse energization by said pulsing relay, a safety relay having a pair of normally closed contacts inserted in said control circuit, a normally open contact with connections to said electromagnetic means, a second relay having a coil serially connected with the normally closed contacts of said safety relay and with said electromagnetic means, an energizing coil on the safety relay, for opening the normally closed contacts and for closing the normally open contact, and means connecting the energizing coils of said safety relay and said second relay with said electromagnetic means so that the current induced by periodic energization and deenergization of said electromagnetic means by said pulsing relay maintains the energizing coils of said safety relay and said second relay energized, said safety relay completing a circuit connection between the pulsing relay and the electromagnetic means when its energizing coil is energized.

4. In combination a reversely operable electromagnetic device, a pair of control lines for said device, a source of pulsing energy and means for applying alternate pulses to each of the control lines, safety means for interrupting the pulses to both sides of the said device if any faulty operation occurs in the pulse applying means, said safety means comprising a pair of relays, each relay having normally closed contacts in one control line and a coil energizable thru normally closed contacts of the relay in the other control line, said relays when energized providing direct connection between the pulse applying means and one side of the reversely operable electromagnetic device, and means connecting the energizing coils of both relays with said electromagnetic device so that the current induced by periodic energization and deenergization of said electromagnetic device maintains the coils of said relays energized.

5. In combination a fluid pressure distributing valve, electromagnetic means for reciprocating said valve, a pair of control lines connected with the electromagnetic means for operating said valve in opposite directions, a source of pulsing energy and means for applying alternate pulses to the said control lines, governing means for differentially altering the length of pulses applied to the control lines, safety means for interrupting the pulses to both sides of the electromagnetic means in the event of any faulty operation of said pulse applying means, said safety means comprising pair of relays having energizing coils, one for each control line, means connecting normally closed contacts in the relay of one control line with the coil of the other relay whereby said other relay coil is energized by the occurrence of a pulse in said one control line, circuit means including normally open contacts engaged when said first relay is energized for directly connecting said one control line to the electromagnetic means around the coil of said other relay, means connecting the energizing coils of said relays with said electromagnetic device so that the current induced by periodic energization and deenergization of said electro- 26 magnetic device maintains said coils energized, and a time delay reactive network operatively connected with said coils for maintaining said coils energized for a predetermined time period after deenergization of said electromagnetic device.

6. In combination, a fluid pressure distributing valve, electromagnetic means for reciprocating said valve, a pair of control lines connected With the electromagnetic means for operating said valve in opposite directions, a source of pulsing energy and means for applying alternate pulses to the said control lines, governing means for differentially altering the length of pulses applied to the control lines, safety means for interrupting the pulses to both sides of the electromagnetic means in the event of any faulty operation of said pulse applying means, said safety means comprising a pair of relays having energizing coils, each of said relays having contacts providing a pair of alternate circuits in each control line between the pulse applying means and one side of the electromagnetic device, one of said alternate circuits including normally closed contacts of one relay and the energizing coil of the other relay, the second alternate circuit comprising an open contact connected with electromagnetic device around the coil of the other relay, and means interconnecting the relays such that a pulse upon either control line energizes the coil and establishes the said second alternate circuit to one side of the electromagnetic device, and means connecting said energizing coils with said electromagnetic device so that current induced by periodic energization and deenergization of said electromagnetic device will maintain said coils energized.

7. In a controllable pitch propeller driven by an engine and having a hydraulic organization for adjusting the blades for governed speed, feathering and negative thrust regimes of operation, a governor controlled, electrically operable valve for adjusting the blades to effect electrical governing at a selected speed, governing means operable upon the governor controlled valve for maintaining a selected speed, electrical control lines connecting the governing means and the governor controlled valve for transmitting control by the governing means to the governor controlled valve, the combination of safety means operatively connected in said electrical control lines for disconmeeting all governor control by the governing means whenever faulty operation of the governing means occurs, said safety means including a pair of relays having energizing coils operatively connected with said electrical governing means in opposite control lines.

8. In an aircraft propeller having adjustable blades, an hydraulic organization carried by the propeller and including an electrically operable, reciprocating valve responding to control signals to adjust the blades in an increase pitch direction and in a decrease pitch direction, a control organization for applying control signals to the hydraulic organization to effect adjustment of the blades for propeller operation at a selected speed Within a governing speed range, means in the control organization for determining the selected speed setting within the governing speed range to which the propeller operation will be governed, said control organization including an electrical governor responding to speed error to provide either an increase pitch signal or a decrease pitch signal, and a pair of control lines connecting the electrical governor to the reciprocating valve for transmission of the governor signals to one side or the other of the reciprocating valve, the combination of an electrical safety device operatively connected in each of said control lines and responding to the transmission of governor signals over the respective control line for completing the path of signal transmission over the other line, and means operatively connecting said electrical safety devices and said means for determining the selected governor speed setting for energizing said electrical safety devices during selection of the governor speed setting to 

